The present invention relates to a technique for fabricating a compound semiconductor device using a silicon (Si) single crystal substrate having a specific azimuth with respect to the plane of the substrate.
As one of Group III–V compound semiconductors, a boron phosphide (BP)-base Group III–V compound semiconductor (boron phosphide-base semiconductor) containing boron (B) and phosphorus (P) as constituent elements is known (see, Iwao Teramoto, Handotai Device Gairon (Introduction of Semiconductor Device), 1st ed., pp. 26–28, Baifukan (Mar. 30, 1995)). The boron phosphide (BP) has a small Philips ionicity of 0.006 (see, Philips, Handotai Ketsugo Ron (Bonds and Bands in Semiconductors), 3rd imp., page 51, Yoshioka Shoten (Jul. 25, 1985)) and is a substance almost comprising a covalent bond. Furthermore, this is a zinc-blende type cubic crystal and therefore, has a band structure of degenerate valence band (see, Toshiaki Ikoma and Hideaki Ikoma, Kagobutsu Handotai no Kiso Bussei Nvumon (Guide for Basic Physical Properties of Compound Semiconductor), 1st ed., pp. 14–17, Baifukan (Sep. 10, 1991)). By virtue of this, boron phosphide is advantageous in that a p-type electrically conducting layer can be readily formed.
Conventionally, various compound semiconductor devices are fabricated by using a boron phosphide layer provided on a silicon (Si) single crystal substrate. For example, a hetero-bipolar transistor (HBT) using a boron phosphide layer is known (see, J. Electrochem. Soc., 125(4), pp. 633–637 (1978)). Also, a solar cell using a boron phosphide layer as the window layer is known (see, J. Electrochem. Soc., supra). Furthermore, techniques for fabricating a blue-band or green-band light emission diode (LED) or laser diode (LD) using boron phosphide and a mixed crystal thereof are disclosed (see, Japanese Patents (1) 2809690, (2) 2809691 and (3) 2809692, and (4) U.S. Pat. No. 6,069,021).
The lattice constant of a monomer boron phosphide (BP, boron monosphosphide) is about 4.538 Å (see, Handotai Device Gairon (Introduction of Semiconductor Device), supra, page 28). On the other hand, the silicon (Si) single crystal used as the substrate is also a zinc-blende type cubic crystal and the lattice constant thereof is about 5.431 Å (see, Handotai Device Gairon (Introduction of Semiconductor Device), supra, page 28). Accordingly, the lattice mismatch degree expressed by the ratio of difference (=0.893 Å) in the lattice constant of both crystals to the lattice constant (=5.431 Å) of silicon single crystal is as large as about 16.6%. In order to prevent peeling of the boron phosphide layer from the Si substrate surface due to this large lattice mismatch degree, technical means of providing a low-temperature buffer layer on the Si substrate surface is disclosed, where the buffer layer comprises a polycrystalline boron phosphide containing an amorphous portion grown at a relatively low temperature (see, U.S. Pat. No. 6,069,021, supra).
In conventional techniques, the boron phosphide-base semiconductor layer is formed using, for example, a silicon single crystal having a surface of {100} or {111} crystal plane as the substrate (see, U.S. Pat. No. 6,069,021, supra). In particular, silicon atoms are densely present on the {111} crystal plane as compared with {100} crystal plane and this is considered effective for preventing boron (B) and phosphorus (P) constituting the low-temperature buffer layer from penetrating into the inside of the silicon single crystal substrate.
However, the distance between {111} crystal planes of the silicon single crystal is about 3.136 Å, whereas the distance of {110} crystal planes of boron phosphide (BP, lattice constant =4.538 Å) is 3.209 Å and does not agree with the distance between {111} crystal planes of the silicon single crystal. Therefore, the boron phosphide layer provided on a conventional silicon single crystal substrate having a surface of {111} crystal plane is disadvantageously a poor-quality crystal layer containing a large amount of crystal defects such as dislocation or stacking fault.
The present invention provides a technique for giving a boron phosphide-base semiconductor layer having excellent crystallinity by using a silicon single crystal substrate having a surface such that the distance between {111} crystal planes of silicon intersecting with the surface of {111} silicon single crystal agrees with the distance between {110} crystal planes of boron phosphide.